The production of silica-filled rubber mixtures, as compared with carbon black-filled rubber mixtures, requires a more protracted mixing process. The higher mixing requirement when incorporating silica, however, could, in principle, be avoided if the silica were incorporated into a rubber solution immediately after producing the rubber. The precipitated silicas currently used for producing tires, however, are not suitable for this type of process without some pretreatment since they are not precipitated when removing the solvent with steam, but largely remain in the water phase.
U.S. Pat. No. 5,166,227 describes a process for producing silica-filled emulsion rubber mixtures in which a dispersion of silica and a rubber latex are spray dried together. This process has the disadvantage that the entire amount of water has to be evaporated involving a high energy demand. In addition, the silica is not activated in contrast to the rubber mixtures in the present invention.
Polysulfidic silanes applied to supports and prepared by reacting halogenosilanes with polysulfides in the presence of a support in water are described in EP-761,742, wherein it is mentioned that these materials can also be used in the non-dried state for preparing rubber/filler master batches. It has now been found, as a new feature, that special requirements have to be placed on the fillers for preparing rubber/silica master batches which are not mentioned or suggested in EP-761,742.